There are many fields of manufacture in which the metalizing of the interior of base bodies, such as pipes and tubes, or segments thereof, of ordinary metals or steel, with an expensive surface layer treatment, or coating, that is fused to the metal, is desirable to provide a finished, or partly finished, part or product that will respond to manufacturing specifications, but which is less expensive than making the entire body of the same material that the specifications require. Thus, parts such as the interior of pipes or tubes, used to convey therethrough corrosive or abrasive fluids, liquids, slurries and the like, and bearings, sleeve segments, or collars are frequently required to provide thereon an interior, or concaved, metalized surface of chromium, or chrome, or other special metal or metal alloy, that will either resist wear or will provide a good bearing surface. For instance, in strings of pipe used in deep oil wells, it is desirable that the interior surface of the pipe have resistance to corrosion or wear, so as to extend the time period that a string of pipe functions without disruption of oil production and consequent increase of costs.
It has been long known that ordinary steels, except for leaded steels or resulphurized steels, may be chrome surfaced, by plating or the like, to both meet the specifications for desired strength of the part and with the surface character being specially adapted for exposure to a harsh environment in which the part is to be used.
However, chromium, for example, is a relatively expensive material, and chromium's use in various chemical baths means, by which chrome plating may be effected, is enviromentally undesirable and/or difficult and expensive to control. Also, it is technically difficult to deposit a metalizing layer of any substantial thickness onto the interior surface of tubes or pipes, or segments thereof, that are to serve as the bearing surface of a bearing or journal element.
While metalizing the exterior surface of bars and rods avoids, to substantial extent, the undesirable environmental effects associated with chemical plating of such bodies, the mechanical metalizing techniques previously employed in metalizing such bars and rods have usually used an open flame torch that burns fuel gases, such as acetylene, propane, or the like in the presence of oxygen, to both preheat the body surface to an elevated temperature and to heat the surface application material, which is initally in powder form, to a temperature at which the powder material will become at least partially molten and fuse onto the base material of the body. These prior art metalizing techniques have not been wholly successful for economically metalizing the exterior of tubes, as the heat of a torch will frequently burn through the wall of the tube. It will be understood that such prior art metalizing techniques generally are not successful in metalizing the interior of elongated tubes and pipes, as access to the interior of such elongated bodies with an open flame torch is very difficult, if at all possible.
The problems with said prior technique for metalizing exterior surfaces are that there is both lack of accurate control of the thickness of the layer of the surface application material to the underlying body, and resultant lack of uniformity of the thickness of the layer that is applied by open torch heat. Furthermore, the minimum thickness of the layer of applied material usually obtained by metalizing with an open flame torch, working with powdered metal, is about 0.008 inches, and maximum thickness of layer of applied metal is about 0.015 inches, both of which thickness values are frequently much greater than the thickness of the applied material layer required to be supplied to meet the performance specifications for the metalized part, and this substantially increases the cost of manufacture. A further problem is that when using fine particles of metalizing materials to form a fused surface on an underlying body, the torch heat intensity is frequently so great that it vaporizes, or burns away, a substantial quantity of the finest particles of the metalizing material, resulting in loss of material and economic waste. Still another problem is that, in the event a thick layer of metalizing is required to be deposited, there is insufficient control over the thickness of metal being deposited, and therefore maintaining of concentricity of the inner surface of a metalized sleeve, or journal is difficult, and machining or other expensive finishing operations must be resorted to in order to obtain a high degree of concentricity of the innermost surface of an arcuate part that has been metalized.
An improved method of metalizing the exterior of metal bodies is disclosed in my co-pending application, Ser. No. 374,282, filed May 3, 1982. This application is directed to the much more difficult problem of metalizing the interior of tubular metal bodies, such as pipes or tubes, and to obtaining a high degree of concentricity of the innermost surface of the metalized deposit on the base body.
One search for prior art relating to concepts disclosed herein has resulted in noting the following U.S. Pat. Nos. Group A. Re. 24,852; 3,158,499; 3,359,943; 4,122,798; 4,197,336; 4,243,699; 4,302,482.
Other searches have disclosed the following U.S. Pat. Nos. Group B. 2,198,254; 2,241,095; 2,289,658; 3,278,331; 4,244,985; 4,324,818; 2,803,559; 2,887,984; 3,108,022; 3,326,177; 3,389,010; 3,560,239; 3,599,603; 3,922,384; 4,082,869; 4,315,883; 2,822,291; 2,845,336; 3,063,860; 3,207,618; 3,218,184; 3,394,450; 3,405,000; 3,532,531; 3,654,895; 3,814,616; 3,974,306; 3,982,050; and 4,169,906.
In Applicant's view, the prior art references of "Group A" are significant as they reflect attempts by others to effect deposition of a protective coating, sometimes metal, on the inner surface of an annular or tubular base member. Other of the prior art patents noted may have some relevance in connection with some of the broad concepts of application of powdered surfacing materials, including alloys, or in connection with the broad concept of metalizing less expensive base materials with a more expensive material. All references known to Applicant are called to the Patent Office's attention to reflect the state of the art, and to advise of Applicant's present knowledge of prior art that was considered by an employed searcher to be worthy of selection. In Applicant's view no single prior art reference, nor any logical combination of multiple prior art references would suggest, to one skilled in the art, the developments and improvements that Applicant discloses herein.